1. Field of the Invention
The present invention relates in general to a molding device and a molding method for molding rotators, such as, a plastic blower fan and the like, and more particularly to a molding device and a molding method for molding plastic rotators of a type that has a center member embedded in a boss portion thereof integrally. More specifically, the present invention relates to improvement in the molding device and molding method by which undesired out-of-centering of the center member relative to the boss portion of the rotator is suppressed or at least minimized.
2. Description of the Prior Art
Among various rotators, there is an automotive blower fan made of synthetic resin, that comprises generally a center boss portion, a plurality of blades radially outwardly projecting from the center boss portion and a die-cast center member integrally embedded in the center boss portion.
For molding such blower fan through an injection molding technique, there has been used a molding device or mold assembly which generally comprises a movable die and a fixed die. Each die has a recess shaped coincident with the external form of one side of a product, that is, the produced bower fan. The movable die comprises a die proper sized to cover the entirety of the produced fan, a recessed center portion formed in the die proper for shaping the center boss portion of the fan, a nested structure formed around the recessed center portion and a center pin projected from the nested structure. The movable die is mountable on the fixed die to define therebetween a cavity that is shaped in coincidence with the external form of the produced fan.
In injection molding, a center member is received on the center pin and the two dies are coupled together tightly. Then, a measured amount of molten resin is poured or injected into the shaped cavity of the die assembly. When the resin is cooled to have a suitable hardness, the two dies are uncoupled to release the product, that is, the blower fan. In this molding, however, the product tends to suffer undesired out-of-centering of the center member relative to the center boss portion of the produced fan.
In order to prevent or at least minimize this undesired out-of-centering of the center member, various measures have been proposed and put into practical use. One of them is shown in Japanese Patent First Provisional Publication 5-116186. In this measure, a positioning device is arranged between the fixed and movable dies, that generally comprises a positioning pin secured to the fixed die and a positioning opening formed in the movable die. Upon coupling of the two dies, the positioning pin is inserted into the positioning opening to assure a relative positioning between the two dies. With this, adequate centering of the center member relative to the center boss portion of the fan is obtained.
However, due to its inherent construction, even the positioning device of the publication has failed to provide the mold operators with satisfaction. That is, it is very difficult and at least troublesome to accurately fix the positioning pin to a right position of the fixed die. In fact, in the disclosed positioning device, four connecting bolts are used for securing the positioning pin to the fixed die. Of course, if such fixing is roughly made, precise positioning between the two dies and thus between the center member and the center boss portion of the produced fan is not expected.
It is therefore an object of the present Invention to provide a molding device for molding a rotator, which can eliminate the above-mentioned out-of-centering of the center member.
It is another object of the present invention to provide a method for molding a rotator, which can eliminate the above-mentioned out-of-centering of the center member.
According to a first aspect of the present invention, there is provided a molding device for molding a rotator that has a center member embedded in a given portion of the rotator. The molding device comprises a pair of molding dies which define therebetween a shaped cavity when properly coupled, the cavity being a cavity into which a molten resin is injected upon molding of the rotator; an insert die fixed to one of the pair of molding dies in such a manner that at least a part of the insert ale is exposed to the shaped cavity when the molding dies are coupled, the insert die including a base block secured to one of the pair of molding dies; a cylindrical holding bore defined by the base block; a plurality of cylindrical eccentric members having eccentric through bores whose eccentric degrees are different from one another, each eccentric member being sized to be intimately received in the cylindrical holding bore; a positioning structure that establishes an angular positioning of selected one of the cylindrical eccentric members in the cylindrical holding bore relative to the base block; a center pin adapted to carry thereon the center member for placing the center member in the shaped cavity when the paired molding dies are coupled, the center pin having one end portion intimately received in the eccentric through bore of the cylindrical eccentric member held in the cylindrical holding bore; and a fixing structure that fixes the center pin to the base block.
According to a second aspect of the present invention, there is provided a method of molding a rotator that has a center member embedded in a given portion of the rotator. The method comprises the steps of (a) preparing a molding device that includes a pair of molding dies, an insert die block fixed to one of the molding dies, a center pin detachably held by the insert die block and a plurality cylindrical eccentric members, the cylindrical eccentric members having eccentric through bores whose eccentric degrees are different from one another, one of the cylindrical eccentric members having an eccentric degree of 0 (zero), and each eccentric through bore intimately receiving therein at least a part of the center pin when molding is carried out; (b) coupling the center pin with the cylindrical eccentric member of 0 (zero) eccentric degree, fixing the couple to the insert die block and setting a center member on the center pin; (c) molding a rotator using the molding die that is incorporated with the couple and the center member; (d) repeating the step (c) while changing the center member to mold a plurality of rotators; (e) measuring imbalance degree of each of the molded rotators with respect to an ideal structure of the rotor, and calculating an average value of the measured imbalance degrees; (f) selecting one of the cylindrical eccentric members and deriving a correction angle needed by the selected cylindrical eccentric member with reference to the calculated average value, the combination of the selected cylindrical eccentric member and the derived correction angle being effective for eliminating the imbalance or at least minimizing the imbalance degree; (g) changing the originally set cylindrical eccentric member of 0 (zero) eccentric degree with the selected cylindrical eccentric member (h) establishing a desired angular positioning of the selected cylindrical eccentric member relative to the insert die block with respect to the derived correction angle; (i) fixing the new couple including the selected cylindrical eccentric member and the center pin to the insert die block and setting a center member on the center pin; and (j) molding a rotator using the molding die that is incorporated with the new couple and the center member.